text:
What are the lowest authorized minimums for each ILS category?
I have been recently told that ILS minimums were changed some time ago. Could anyone tell me what the lowest authorized ILS minimums are for CAT I, CAT II, CAT IIIa, CAT IIIb and CAT IIIc? I'm interested in FAA, EASA and ICAO standards.

Minimums are specific to the approach in question and vary based upon their specific location and circumstances.

You should provide the current state of your research about this topic to allow us to answer in a specific way.

Since this has been edited to ask for the "lowest authorized minimums for each category", I believe that it is a good question and should be reopened.

As Carlo mentioned in the comments, the minimums may vary from place to place to place. Here in the US you can find all that information here. Or you can buy a printed copy from a variety of aviation suppliers.
This order published in 2012 sets some minimum performance guide lines for minimums as well. For example,

(2) The following is the minimum class of performance (refer to
  Appendix B) required for an ILS to support a published Title 14 of the
  Code of Federal Regulations (14 CFR) part 97 CAT II or III SIAP:

Class II/T/2 for operations not less than RVR 1200.
Class II/D/2
  for operations not less than RVR 1000.
Class III/D/3 for
  operations not less than RVR 700.
Class III/E/3 for operations not
  less than RVR 600.
Class III/E/4 for operations less than RVR 600.

See appendix B in that order for more information.
This may also be of some interest.

Minimums are specific to the approach in question and vary based upon their specific location and circumstances.
However:
AIM 1-1-9 3i states that ILS minimums cannot be lower than as follows for specific categories.
CAT I - 200ft AGL, 2,400ft RVR.
Special Authorized CAT I - 150ft AGL, 1,400ft RVR, if equipped with a FD or HUD.
CAT II - 100ft AGL, 1200ft RVR, using autoland or HUD to touchdown.
Special Authorized CAT II - 100ft AGL, 1200ft RVR, using autoland or HUD to touchdown.  ALSF-2 lighting not required on the field.
CAT IIIa - <100ft AGL, RVR greater or equal to 700ft
CAT IIIb - <50ft AGL, RVR greater or equal to 150ft
CAT IIIc - ZERO-ZERO.  No DH or RVR limitations.
Keep in mind these are MINIMUMS.  Follow published approach plate minimums for specific approaches.  If you attempt an approach to minimums in hard IFR, you better:

Make sure your aircraft is equipped with the required avionics for the approach, the airport in question is equipped for that type of ILS approach, and there are current approach plates for flying it.
Check the aerodrome NOTAMS for notices that said approach equipment is not down for maintenance, etc.
Be VERY proficient in flying instrument approaches and the specific approach in question.
Have a back plan for your backup and fuel to spare.

Ignore that, and you're likely to star in your very own NTSB report.

When authorized by OPSPEC you can have 1800 RVR cat I, 1000 RVR  cat II.

In general, based upon avionics.  Aircraft equipped with approved flight directors or head up displays can shoot these approaches in these conditions.

@CarloFelicione -- Cat I to 1800 RVR is possible w/o avionics support if you have ALSF-2 + TDZ/CL available

That's going to be up to the individual airport authorities and the FAA.  They might approve an approach under these circumstances; I've just never seen a plate like that.  It's going to be a Spec Auth Cat I approach.

@CarloFelicione -- try KORD ILS 9L for instance -- as a general rule, you'll find flat 1800 RVR CAT I wherever a runway supports CAT III ops, at least in FAA-land.

@CarloFelicione -- furthermore, the KORD ILS 9L SA CAT I is a 1400 RVR/150' DH approach.

what is your point?

@CarloFelicione -- that they exist and it's good to be aware of them (also, that the FAA should update the AIM :P)

In fact, CAT I, CAT II, and CAT III are not ILS categories but approach categories. They are described by minimum visibility and decision heights. In the past typically ILS was used for these kind of approaches, but there are other technologies available that support low visibility operations.
From ICAO Annex 6 Part I (International Commercial Air Transport, Aeroplanes), Ninth edition - July 2010:

Category I (CAT I) operation. A precision instrument approach and
  landing with:

a)   a decision height not lower than 60 m (200 ft); and
b) with either
  a visibility not less than 800 m or a runway visual range not less
  than 550 m.

Category II (CAT II) operation. A precision instrument approach and
  landing with:

a) a decision height  lower than 60 m (200 ft), but not lower than 30
  m (100 ft); and
b) a runway visual range not less than 300 m.

Category IIIA (CAT IIIA) operation. A precision instrument approach
  and landing with:

a) a decision height  lower than 30 m (100 ft) or no decision height;
  and
b) a runway visual range not less than 175 m.

Category IIIB (CAT IIIA) operation. A precision instrument approach
  and landing with:

a) a decision height  lower than 15 m (50 ft) or no decision height;
  and
b) a runway visual range less than 175 m but not less than 50 m.

Category IIIC (CAT IIIA) operation. A precision instrument approach
  and landing with no decisoin height and no runway visual range
  limitations.

In Europe, the EASA OPS (EU legislative website)(English PDF) define the categories as:

(12) ‘category I (CAT I) approach operation’ means a precision
  instrument approach and landing using an instrument landing system
  (ILS), microwave landing system (MLS), GLS (ground-based augmented
  global navigation satellite system (GNSS/GBAS) landing system),
  precision approach radar (PAR) or GNSS using a satellite-based
  augmentation system (SBAS) with a decision height (DH) not lower than
  200 ft and with a runway visual range (RVR) not less than 550 m for
  aeroplanes and 500 m for helicopters;
(13) ‘category II (CAT II)
  operation’ means a precision instrument approach and landing operation
  using ILS or MLS with:

(a) DH below 200 ft but not lower than 100 ft;
  and
(b) RVR of not less than 300 m;

(14) ‘category IIIA (CAT IIIA) operation’ means a precision instrument
  approach and landing operation using ILS or MLS with:

(a) DH lower than 100 ft; and
(b) RVR not less than 200 m;

(15) ‘category IIIB (CAT
  IIIB) operation’ means a precision instrument approach and landing
  operation using ILS or MLS with:

(a) DH lower than 100 ft, or no DH; and
(b) RVR lower than 200 m but not less than 75 m;

There is no IIIC defined in the EASA OPS

Whether an operation in low visibility is possible of not is depending on a number of factors:

The quality of the aircraft's navigation/guidance system
The quality of the ground or space based system providing the navigation signal
The training / approval of the flight crew
Local factors such as terrain around the airport, installed lighting etc.

All these factors have an effect on the minima for a specific approach.

EASA Aerodrome Certification Specifications Issue 2 (https://www.easa.europa.eu/document-library/certification-specifications/cs-adr-dsn-issue-2) does define CAT IIIC operations. The definition is the same as the ICAO one.

This gets a bit fiddly, because it depends on not only the ILS equipment available, but on the airport approach and runway lighting environment, the avionics available on the aircraft, and whether the operator has the necessary qualifications for the approach.  (All approaches listed as "SA" require a specific OPSPEC/MSPEC/LOA approval.  Standard CAT II and III approaches are available through blanket OPSPEC/MSPEC/LOAs.)
For FAA-land, though, here are the general rules, assuming no modifications due to obstacles penetrating the TERPS approach surfaces (34:1 or 20:1):

200' DA with 3/4mile visibility (4000 RVR) -- basic CAT I ILS with no approach lighting available (or substandard approach lighting such as MALS, SALS, or ODALS) and no special avionics support.
200' DA with 1/2 mile visibility (2400 RVR) -- CAT I ILS with MALSR/MALSF, ALSF-1, or SSALR/SSALF available, but no special avionics support.
200' DA with 1800 RVR -- CAT I ILS with MALSR, ALSF-1, or SSALR available and the use of command or automatic guidance (FD/AP/HUD) to DA.  This is not a SA procedure -- it is charted as a text note on the standard ILS approach, and is available to all suitably equipped operators.
200' DA with 1800 RVR -- CAT I ILS with MALSR or ALSF-2 + TDZ/CL.  This is the standard ILS procedure minimum for a runway so equipped.  This is also the absolute lowest minimum available for a single pilot operation -- single pilot operators are ineligible to use CAT II/III or SA CAT I/II ILS approaches.
150' DH with 1600 or 1400 RVR -- SA CAT I ILS with MALSR or ALSF/2 + TDZ/CL and the use of HUD guidance to DH.  Most approaches like this are 1400 RVR -- 1600 RVR versions are only present when TERPS demands an adjustment for close-in obstacles.
100' DH with 1200 RVR -- CAT II ILS with ALSF-2 + TDZ/CL.  This is the baseline CAT II procedure, and can be flown by any operator that meets the regulatory requirements for CAT II operations.  Requires a Class II/T/2 ILS.
100' DH with 1200 RVR -- SA CAT II ILS with MALSR/MALSF and the use of HUD or autoland to touchdown.  Requires a Class II/T/2 ILS.  Close-in obstacles may require autoland operations to touchdown.
100' DH with 1000 RVR -- CAT II ILS with ALSF-2 + TDZ/CL and the use of Autoland or HUD to touchdown. Requires a Class II/D/2 ILS.  Not denoted as a SA procedure, but requires OPSPEC, MSPEC, or LOA approval -- it is a chart note on the CAT II procedure instead.
700' RVR, no DH -- CAT IIIa ILS with the use of a fail-passive autoland or HUD system.  Requires a Class III/D/3 ILS and SMGCS.
600' RVR, no DH -- CAT IIIb ILS with the use of a fail-operational autoland system.  Requires a Class III/E/3 ILS and SMGCS.
300' RVR, no DH -- CAT IIIb ILS with the use of a fail-operational autoland system.  Requires full TWY lighting with controllable stop bars, a Class III/E/4 ILS, and SMGCS.  May require surface movement radar.
Operations below 300' RVR currently do not exist, except through special approval.


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Elliptical cross section fuselage
Could someone help me understand the mathematics involved in Elliptical cross section fuselage that are used in A380. Also how double bubble cross sections are calculated.

You need to be more specific. Pressure? Aerodynamics? Cargo volume?

Related: Could some one explain me with the mathematical relations on how the double bubble fuselage cross section (example A380) is designed? and Why is the fuselage on an airliner circular-shaped?

It seems that you've posted this question before and it was closed as "unclear what you're asking". Rather than ask the same question again, please think about how you can edit your original question to explain it better and be more specific; that will help you to get a better response.

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text:
On a chart, how can I find the frequency for flight following?
Is there a map I can refer to in order to pick up the correct frequency for VFR flight following while enroute? I know I can request a frequency from ATC as I depart, but what if I want to fly around and do sight seeing, practice maneuver for my checkride etc. for a while, then pick up flight following for the remainder of the trip?

In the United States, you can consult the VFR Sectional Chart and look for the frequency box located near a terminal area.

Otherwise you'll need to consult the Airport Facility Directory for the region your are flying to find a ARTCC (Center) frequency.

You can also ask flight service.  They are very helpful!

Good point, but how do you find the frequency for the FSS? ;)

The easiest way for light airplanes (which aren't flying at high altitudes) is to call Flight Watch on 122.0.

As I mention in my own answer, I prefer the tabs on the chart because it includes the direction and the operating times along with the frequency. In the KIND example, the tabs have a different frequency for E and W of the active runway, which I find more helpful than looking at the white box on the map. http://skyvector.com/?ll=37.13655803017531,-91.77824375909366&chart=21&zoom=3

Also, the tabs are more comprehensive, since they provide frequencies for radar services at military bases. If you use the maps, heading NE-bound from the SF Bay Area, it says contact Norcal. When you call Norcal, they will just turn you over to Travis. But if you look at the tabs instead of the map, you'll see that Travis has its own approach control, and they provide radar services.

@Lnafziger Flight Watch is gone :-(

There are three types of ATC service: terminal, approach control, and center (ARTCC).
Since you said you're en route, you'll want either approach control or center.
If you're inside the Mode C veil (but obviously not already in the airspace) of a Class B or Class C, or if you're near a military base (which all have radar, 'natch), you'll watch to contact approach control, whose frequencies can be found on the tabs of the sectional, such as this example from San Francisco:

If you're not within the Mode C veil, call up Flightwatch 122.0.
Flightwatch is manned at all times, but it usually takes them at least 5-10 seconds to respond because its infrequently used and they're busy with other things.  The trick is not to make your request on the first call up, but do announce your position, since Flight Service has many transmitters, and they will pick the one that is closest to you:

N347T: Flightwatch, Mooney 3-4-7-Tango, Crazy Woman
  10 seconds pass...
  Fligihtwatch: Mooney near Crazy Woman, Flightwatch, go ahead (they probably won't get your numbers, but they will pick out your type and position)
  N347T: Flightwatch, Mooney 3-4-7-Tango, what's the frequency for flight following near C-Z-I?
  Flightwatch: 4-7-Tango, for radar services near C-Z-I, contact Salt Lake Center on ....

Many GPS units have a "nearest" function that will provide frequencies for the nearest FSS or Center:

I assume you're in the US? If you got flight following when you departed from a controlled field then ATC should tell you if you need to change frequency, unless of course they have to stop providing you the service because of workload or whatever.
In general, flight following is provided by the nearest TRACON or ARTCC, so you can look in at least three places, two of which are maps:

The VFR chart, if you're near a controlled field, which shows the TRACON frequencies
The IFR en route chart, which shows the ARTCC frequency for your general area even if you're not close to a controlled field
The Chart Supplement, if you're near a controlled field

Even if you're near an uncontrolled field, the AFD has a the frequency of the controlling agency/agencies for every field.

@StallSpin That's correct, I really meant to make the point that if you're not 'near' any field then you still have a way to find it. Whatever 'near' means, of course :-)

My own experience with flight following, from operating out of both towered and non-towered fields in the Carolinas:  After taking off on an XC from my non-towered home field, depending on my heading, I contact the nearest approach control, for example, Wilmington NC (KILM) or Myrtle Beach (KMYR). Before taking off from a towered airport, I will ask the ground controller for FF and get a squawk code and post-departure contact frequency. (ATIS at some of airports I have flown into include instructions for requesting FF); to back that up, if I have not already requested FF, ground or tower controller may be proactive and offer it to me.  Airspace around busy airports can be crowded, and I feel safer knowing that I am not an unidentified blip; ATC knows where I am, and what I am doing, and can redirect me if necessary. Positive communication is key to staying safe.

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How do Hoerner Wingtips work?
I was just reading up about different methods of reducing drag through the different wingtip designs when I come across Hoerner Wingtips.
So after some research, I have two questions.

According to this article on pg 1, it states that "The convex underside accelerates the speed of the air passing under the tip to a velocity more equal to that of the air flowing over the top of the tip, thereby creating streamline flow." How exactly does acceleration of air occur just by having a convex underside?
As we can see, the effective wingspan using Hoerner Wingtips can be increased without increasing geometric wingspan.

How does a Hoerner Wingtip enable vortices to be generated further away, therefore increasing effective wingspan?

Thank you! :)

How exactly does acceleration of air occur just by having a convex
  underside

Just like the curved forward surface of a wing does it. Imagine for a moment that the air flows along a straight path: Now it would "see" that the surface below it curves away from its path of travel, and if that path would remain unchanged, a vacuum between the wing and the air would form. Reluctantly (because it has mass and, therefore, inertia), the air will change course and follow the wing's contour. This requires lower pressure, to make the molecules overcome their inertia and change direction.
Near the tip the flow has a sideways component, flowing away from the center on the lower side. This sideways flow, coupled with the sideways curvature on the lower wingtip, creates suction. This area of lowered pressure will suck in more air from inside. In essence, the curved lower side of the Hoerner wingtip extends the suction which is found on the upper surface of the wing to the side of the wingtip.

As we can see, the effective wingspan using Hoerner Wingtips can be
  increased without increasing geometric wingspan.

Well, that is at least what Hoerner claims. Maybe it does move the peak suction of the wingtip vortex a little outside, but this has no effect on the flow field behind the wing and the eventual location of the trailing vortex. Below is a graphical overview of different wingtip shapes and their sideways location of the core of the tip vortex.
Wing-tip shape and tip-vortex location for a family of wings (picture source)
However, this is not relevant for induced drag. In the end, the strength and width of the rolled-up vortex sheet behind the wing indicates the amount of induced drag. Induced drag itself is the horizontal component of the resulting pressure forces on the wing (see here or here for more on that). The tip vortex is sucked into that vortex system regardless of its initial location. See below for an illustration:

B-747 with contrails (picture source)
You can see that the outer contrails of this Boeing 747's engines wrap around the contrails of the inner engines. This shows how the air is pushed down in the wake of the wing and that the centers of the vortices are slightly inboard of the contrails of the outer engines.

That photo is the best illustration of vortex behavior ever. You can really see the sheet rolling up from the sides behind the plane

@TomMcW: Yes, and there is so much more to see: The initial widening of the distance between the inner contrails shows how much they are already pushed sideways (instead of straight down) by the downward-moving air in the center. The very high relative humidity that day produced both strong engine contrails and a visible aerodynamic contrail. The mist in the middle is from condensation in the low-pressure center glinting in the sunshine.

Wings create a miniature weather system around themselves. The Angle of Attack pressurizes air under the wing and depressurizes it over the wing. Air seeks to equalize this pressure all around the wing at the speed of sound -- faster than the wing travels, slowed by the momentum shift (acceleration) of new air entering the system. So in front of the wing air below is pressurized below the altitude of the wing and air above the altitude of the wing is depressurized. This pressure difference creates an updraft ahead of the wing. The wing constantly flies into an updraft of its own creation. You can see this in the rise of streamlines ahead of the wing in wind tunnel tests. The slipstream dividing air that flows over vs. under the wing strikes the underside of the leading edge of the wing, well below where one would expect, if you ignore the weather-like effects of the wing on air around it.
Outboard of the wingtip, this same pressure difference releases pressure outward below the wing and pulls air inward above the wing, creating the vortex. The convex ramp of the Hoerner wingtip changes the angle of momentum of this outward flow of air, and makes the outward flow below and inward flow above asymmetrical. The center of the vortex is higher and farther outboard of the wingtip.
Lift is amplified beyond the cord of the wing by the thin, turbulent boundary layer behind the wing, ended by the wingtip vortex. Air pressure differential maintained by this boundary layer is a major contributor to lift. This is why Ground Effect happens. If the boundary layer strikes the ground before it disintegrates tens of yards behind the wing, the wing generates more lift and less drag. Move the vortexes out with Hoerner wingtips, and that boundary layer effectively acts like an extension of the wing lengthening the wingspan. Air mass can't flow through that invisible boundary layer any more than it could flow through the wing, and that pressure difference is where lift comes from. The boundary layer maintains that pressure difference, just like the wing does.


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Why do flaps affect Vmc?
While looking at several Type Certificate Data Sheets for business jets, I have noticed that there is a common theme relating to their VMC in that the VMC (airborne) are lower when the flaps are deployed than when the flaps are retracted.
I have heard this effect accounted for in light piston twins through the process of only one engine producing thrust and propeller wash over one of the flaps, thus creating a differential drag on either of the flaps. With only one engine accelerating air over the wing and associated flap, the two flap panels would effectively see different airspeeds and resultant drag values such that there was a stabilizing yaw force created.
This explanation doesn't seem to apply to the business jets as they have engines mounted to the rear of the fuselage and therefore have no flap to “blow over” as in the case of the piston twins.
It appears there is little to no information available in several textbooks and online sources I have perused trying to figure out how this works. The “what” is answered easily, it's the “why” that remains elusive.
This leads to the question: how does flap extension affect directional stability and the associated VMC (airborne)?

Well, I dont know :) but I offer two educated guesses: At least for A320 the increasing flap setting decreases VMCG so could it be that the "net thrust" of the remaining engine is lower with higher drag, thus requiring less authority from rudder to maintain dierctional control. My other guess is that the flap setting affects the airflow around empennage and thus alters rudder effectivity.

Can you give some examples of business jets that have lower Vmc with flaps down even though their engines are aft of the flaps? The first few I checked list only one Vmc regardless of flaps setting.

Don't know about business jets, so not an answer but a comment. In the C-130, the hydraulic pressure to the rudder is reduced when flaps are up so as to avoid over-controlling the rudder. There may be a similar pressure-reducer at work in the jets you're seeing, where in order to give the rudder more authority at low airspeed, the pressure is greater with flaps extended than with flaps up. Also, I'd expect VMC's with tail-mounted engines to be much lower than with wing-mounted engines (which have more moment-arm, i.e. leverage), vis-a-vis the rudder. Can you link to the data you're looking at?

Good point @RalphJ.  Also worth noting, the EA-6B had extended rudder throws with flaps down due, (if I remember right...) to a mechanical rudder stop retracting.  It's likely that these sort of features answer the question, but the details are probably aircraft specific.

The bottom line up front is static Vmc is a function of more than just directional stability. It’s a full 6-DoF trim that’s impacted by many variables. Side, normal, and axial forces have to balance (net zero) as do rolling, pitching, and yawing moments. For a given speed and weight, etc., adding flaps results in more lift and hence less angle-of-attack (AoA) is required to trim. On most configurations, rudder and roll control effectiveness are decreased at higher AoA’s. Therefore, with the flaps extended there is more roll and yaw power available to trim at a larger sideslip angle.
Vmca is very airplane and configuration-dependent, especially since it can be set by multiple factors. For example, pedal force or rudder power limits may be reached before the 5 deg of bank limit. So, it’s not just about directional stability or even aerodynamics generally but also the propulsion system, mass properties, and flight control system. Furthermore, there are both static and dynamic requirements. So, yes, it is complicated.
FAA part 25, section 149(a) through (d) describe FAA Minimum Control Speed, Vmc (also known as Vmca) requirements and AC 25-7D, Flight Test Guide for Certification of Transport Category Airplanes provides valuable additional information.

This answer is, more or less, "It's really complicated and I don't understand ..."  The sentence that starts with "For a given speed and weight, etc., adding flaps results in more lift and hence less angle-of-attack (AoA)... " is the beginnings of the correct answer, but the ability to trim is not a factor.

No, it's complicated and I do understand. The static requirement is evaluated by the FAA in flight test where the goal is to fly a constant heading at constant speed and the prescribed contstant engine settings and evaluate what the steady state values are for bank angle, etc. "Trim" is common term in aerospace engineering used to refer to a static flight condition, usually (but not always) zero angular rates and accelerations. It does always refer to time-invariant inceptor inputs. Note this is not the same as 'trim' as in reducing control forces by use of tabs or other means.

No, it's really simple.  Higher drag requires more power. More power (with only one engine running), means more yaw (sideslip) At or near clean Vmc, you are in a high AoA, High drag regime. You require close to full rudder to maintain directional control. Putting the flaps down means lower AoA, less drag, less asymmetric thrust, and so you now have excess rudder available to maintain control. So your Vmc is lower.  I don't understand what trim has to do with this. If you are using an engineering term (other than the common GA understanding), you can't just throw it out without explaining it.

I have never heard an adequate explanation of this as well.  Charles Bretana hints at an idea here.  I might offer that flaps, in altering the overall camber of the wing, decrease the stalling “speed” of the wing i.e. reducing the AoA, thereby increasing control authority at lower speeds, allowing the pilot to maintain directional control than would otherwise be possible with a wing in a cruise configuration.  Another safety advantage here is that, in reducing stalling speed, it helps gives a larger margin between speeds when rudder authority is lost and when the critical AoA is exceeded, reducing the risk of a stall in an uncoordinated condition.

A simpler answer is that flaps lower the Angle of Attack necessary to produce the lift to maintain 1-G level flight at any specific airspeed. So they reduce the minimum airspeed necessary to maintain level flight. At low airspeeds (where AOA is above L/D max AOA), induced drag increases as you slow, so drag is lower at this lower AOA. This means power required to maintain that airspeed is also lower. This is why this is called "behind the power curve".
The lower the power output at the point an engine fails, the less asymmetric thrust there will be. So with the flaps down, you can slow to a lower airspeed than you can with flaps up, and still maintain direction control if/when an engine fails.

Vmc is always defined with the operating engine at a specific critical power level, isn't it? I'm also very skeptical of your assertion that it takes less power to maintain airspeed with flaps down. Flaps increase drag, which increases the power required to maintain a given airspeed.

Yes, flaps increase drag at a given airspeed and AOA, but if you are at high AOA, (like close to a stall) with flaps Up, putting them down increases the camber of the wing, and increases Lift  (and drag) but if you lower the AOA to get back to the same amount of Lift (whatever is required to maintain level 1-G flight), then the AOA and drag will be substantially lower.

.. and VMC is defined (as I recall) as the minimum airspeed at which directional control can be maintained on only the critical engine running at that power setting required to maintain level 1-G flight at that airspeed. At any lower airspeed, drag is Higher, so yaw/sideslip due to asymmetric thrust is higher, rudder effectiveness to counter the yaw is less, so the VMC for this higher drag AOA will be higher.

@Romeo understands... You can fly slower with the flaps down. Clearly, drag, in any configuration, in this regime increases as airspeed decreases closer to the stall (Clmax) AOA. So with both engines running or not, you can fly slower with the flaps down. If you are at or near Vmc and an engine fails, putting the flaps down immediately reduces the AOA (and power) required to maintain level flight. With less power, you have less asymmetric thrust, so you can slow down more, (not that you'd want to!), and still maintain directional control

That may be true when you're very close to a stall, but in general flaps increase drag more than they increase lift. Flaps steepen an airplane's glideslope exactly because they make level flight require more power.

But also Vmc is defined with "Maximum available takeoff power or thrust on the engines;" and Vmcl is defined with "Go-around power or thrust setting on the operating engine(s)" so that isn't relevant anyway unless the deployment of flaps on the type in question limits the available power.

@Chris, But that's exactly what we're talking about when we're discussing Vmc.  A High AoA, Low airspeed situation where rudder effectiveness is low, (because we're slow), and drag is high. (behind the power curve). We can fly slower with the flaps down! Why? because the high camber flaps down wing produces more lift and lower induced drag than flaps up wing. True, the Flaps down wing has higher form drag than the flaps up wing, but at slow airspeed (behind the power curve most of the drag is Induced drag, (drag due to Lift), and this is much higher with flaps up, since AoA is higher.

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What is the purpose of the fin at the Boeing 787 APU exhaust?
The fin is located under the Boeing 787 APU exhaust as shown in the picture below. Does anybody know the application of this thing or it is used for 'guiding' the APU exhaust? Thanks.

APU fuel drip shield.

At a guess it’s an aerodynamic fence of some sort, most likely added during flight test as a band aid against unwanted turbulent airflow in that region.  It’s a relatively simple fix for bad aerodynamic design

It's a bib for the APU to stay tidy.

@Pritam: What about writing an answer? Here is more information you can use (it prevents torching).

My guess is, because of the shape of the tail, air will be flowing up and meet the horizontal flow. If there is a hole in the middle there will be a lot of turbulence so they added a deflector to let them mix slowly. For a plane of this size this is more likely to reduce noise or improve the efficiency of the APU.

It's primary purpose is noise abatement. NASA has been encouraging mfg to install similar shielding plates near other parts of the aircraft such as the whistling wheel brake parts. The flying wing concept has the engines above the fuselage (for ground noise blocking) for the same reason. During landing, the airframe is louder than the engines. NASA has several high profile noise abatement research projects such as QAT. https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20130013127.pdf and https://www.nasa.gov/centers/langley/pdf/70882main_FS-2002-09-73-LaRC.pdf

@jwzumwalt The article mins linked shows it has nothing to do with noise. It's to avoid a flamethrower when they start it up.

Gas turbines don't spit flames out the back when they start up unless something has failed, and a shield on the exhaust wouldn't stop that anyway.

All gas turbines including APU's have a drain tube from the combustion chamber that will drain excess fuel onto the ground. If there was any excess fuel in this APU, the slope of the exhaust would pool it in the engine and that fairing would not have any effect - nobody would stand for that.

As mentioned in the comments, this is indeed an "aerodynamic fence."  Fences of this sort serve two purposes:

Direct airflow; or
Energize (or trip) boundary layer airflow.

The latter are normally perpendicular to the surface on which they are mounted, allowing them to protrude directly into the boundary layer of air flowing over the surface.  You can picture the effect of these types of devices by looking a how water flows over and around a boulder in a stream or river.  "Tripping" the flow mixes the boundary layer with the more energetic air outside the boundary layer.
It is most likely the former, a device used to direct the airflow.  By the time air gets to the tail of an airplane, to the aft most part of the empennage, it is quite unsteady flow. (In this case, imagine the water flow behind a large ship.) The turbulence characteristic of this type of flow can wreak havoc for designers who want to vent exhaust gases or airflow out of the aircraft's APU. This turbulent flow can create stagnant zones which would block the air from exiting the way intended, as described here.  By directing the flow of the air around the exhaust duct, this can be minimized or avoided altogether.  There is, however, probably a small amount of the boundary layer that gets energized by this device, which would further help the designers manage the flow.
The article previously cited calls them vortex generators, which are explained in more detail here and correspond to 2 above.  Fuel that was pooling in the APU was a result of the stagnation of the flow.

Can you cite a source to back up your answer?  The article that @mins linked in comments to the OP indicates that the purpose is to allow fuel to exit the tailcone during flight rather than pooling in the tailcone.  What you describe regarding airflow is consistent with that explanation, but you're talking about exhaust gasses; the article about fuel before the APU is turned on. Can you provide sources for your answer, and/or additional clarification, reference that article?

Actually, it is more likely that unburned fuel pools after the APU is shut down and would re-ignite once the APU is restarted.

Albeit being a technically perfect answer, it does not answer the question and it is actually formally wrong: vortex generators and/or strakes and/or fences and/or... are used to improve the airflow on the surfaces behind them. Behind that fences there's nothing, so its purpose is anything but aerodynamics... The only aerodynamic thing that it is doing is most probably producing additional drag

StackExchange is so funny sometimes!
It is to simply keep fuel from the body drain tubes out of the APU exhaust.

Please edit your answer to include a reference. You could e.g. use this link that mins already linked to in 2017.


text:
Why do some turbofan blade have forward swept tips?
I notice that in Trent700  engine fan blade there is no curve extension at the tip unlike in other engine's fan blades such as the GE90 ,T900 etc.
What are the purpose of it?

Trent 700 without forward swept blade tips

Engine with forward swept blade tips

These two images look to be exactly the same?

Do you mean the tips of the blades are swept forward in some parts of some engines but not others and you want to know why it's done?

This may be about the absence of mid-span snubber.

Hello Ajas, welcome to Aviation.SE. I have edited your question by including the Trent 700 image from your duplicate question and clarifying the question. I hope it now reflect what you wanted to ask. Please don't post duplicate question, instead use the  link below your questions to make clarifications if needed. Could you also add the photo source and credit the photographer below each image?

I have another question: why are the tips here forward swept, but not swept backwards like the  wing? What are the differences in aerodynamic properties?

Increasing performance of the fan means making it rotate faster. Tips of the fast-rotating fan travel at supersonic speeds. This design of fan blades is to overcome blade stall and to increase effectiveness of the fan. The design is probably patented and that's why it doesn't show up on engines of other manufacturers.

Here is a related patent:  https://www.google.com/patents/US6071077


text:
Do new VHF radios need to be flight tested?
I'm in the process of upgrading all our VHF radios and the local regulator has asked us to follow the guidance/recommendations from ICAO, as we have more or less cancelled many of our local rules. The radios will be used for voice only (including Volmet and ATIS).
What do the ICAO recommendations/procedures say about installing new air-to-ground VHF radios? Do they need to be tested by a test flight? Is there a difference if it is a new installation with new radios and new antenna, versus new radio types but with the same antenna, same frequency and same power output?

Welcome to aviation.SE! In case ICAO has no specific guidance (or no one here knows), would it be helpful to get an answer for a particular country or regulator? If so, you can edit your question to add that.

In case that matters, does your question include equipment used for data transfer (VDL)?

So your local regulator is making you do their job for them?

Avionics shops almost never test VHF radios in flight. They are almost always tested on the ground with test equipment. The only time I can think of an in-flight test being required is if the technician is trying to troubleshoot an intermittent problem that only happens in flight (such as a faulty connector in the vibration-rich environment of a military transport helicopter).

You can test the VHF radios and any Avionics systems following the AC 25-7D.


text:
Do all aircraft need to have horizontal and vertical stabilizers?
Are (or were) there any operational aircraft that don't have horizontal and vertical stabilizers or canards? If so, what's the effect on how they fly?

You are asking if you can take any aircraft and remove its elevators/stabilizers and it would still fly normally? No, absolutely not.

Possible duplicate of What is the function of the tail section on a fixed-wing aircraft?

@RonBeyer That's not what is being asked at all.  The question is clear.  Are there, or were there any aircraft that don't have stabilisers or canards.  The short answer to which is yes.

@Simon Given the original title and text, its not so clear, which is when the comment was made.

Related: Tailless aircraft design.

You always need to have pitch, roll and yaw control. Vertical and Horizonal stabilizers are just a solution. Flying wings have another solution.

Just to be a little too precise :-) , the original title referred to elevators/stabilizers, no mentions to rudders or fins (at least that's how I understood the question). I was thinking of replying (but had no time to reply) mentioning Mirages or Convair's "delta-winged" fighters other than the various tailless design in the answers.

There was a design for a paper plane without vertical or horizontal stabilizers : it maintained stability using the shape of the wing - search for it I could not find in my search engine.

Depending on how you classify the control surfaces, the B-2 Spirit does not have a horizontal stab, since it is a "flying wing" design.  As you have changed the question, the other part of the answer is that the flying wings have been able to get by without vertical stabilizers as well, at least in the case of the B-2. It uses both spoilers ("split brake rudders") and thrust differential to accommodate the lack of a vertical stabilizer.

Northrop had investigated several means of applying directional
  control that would least infringe on the aircraft's radar profile,
  eventually settling on a combination of split brake-rudders and
  differential thrust ~  Sweetman, Bill. "Lockheed Stealth" (2005) ISBN 0-7603-1940-5., p. 73

(And as with flight controls in general on the on B-2, that's helped a lot by its fly by wire flight control system).

As the Germans discovered in their flying wing aircraft (Ho229), and the USAF in the YB-35 and YB-49 programs, flying wings have inherent instability, even though some early biplane "flying wing designs" were stable enough to fly. (Dunne).

The B-2 has a fly by wire system to retain stability and handling qualities so that it does not have to make tradeoffs (loss) in performance that earlier flying wing designs did in order to make the design "stable enough."
What the elevator/horizontal stab do for conventional aircraft is allow for longitudinal control (pitch control).  If you don't choose to use that conventional method, the "effect" is that your design must find another way to establish longitudinal control and stability or the aircraft risks being unstable in that axis.
Likewise with vertical stabilizers, your design has to address stability in the yaw axis if you want to make it without a control surface acting in that axis.

Can you expand a bit on how the B-2 achieves yaw stability? i.e. what actuators does this smart fly-by-wire use to control the plane - is it just differential thrusting on the engines?

That, and differential control surfaces. Basically. There's more to it than that, but that's the gist of it. There are a total of 9 independently movable control surfaces at the trailing edge of the wing. 3 pairs of elevons, 1 pair of split brake-rudders, and an elevator in the middle.

@E.P. Edited in.

@E.P.: You can see in the picture above. The split ailerons at the end of the wings are called drag rudders - differentially increasing drag on either side of the wings. Opening both drag rudders shifts centre of drag backwards instead effectively acting as vertical stabilisers as well (think about how badminton shuttlecocks achieve directional flight)

Based on the wording of your question, the Flying Wing design would qualify. These aircraft do not have proper "tail" stabiliser sets and they still fly.

Among the earliest aircraft to fly were the models of Alphonse Pénaud, and they flew without a vertical tail. The rubberband-powered pusher propeller was sufficient for stabilization. Admittedly, they did not need to maneuver.

Pénaud's Planophore (picture source). The spinning propeller replaced the vertical tail.
After Friedrich Ahlborn published a study on the aerodynamic qualities of the Alsomitra seed, Igo Etrich and Franz Wels designed a glider inspired by the seed's shape. This flew in 1906 and was the first man-carrying flying wing. As a glider, it could not rely on a pusher propeller for stabilization; instead it copied the sweptback outer wing of the Alsomitra seed with its upswung trailing edge.
Flying wings use reflex airfoils and/or wing sweep in combination with reduced incidence in the outer part of the wing (washout) for stabilization. Yaw stability is provided by sweep and pitch stability by the reduced incidence in the outer/rear part of the wing. In general, avoiding tail surfaces altogether can still result in stable aircraft but reduces damping a lot. The result is a flyable but problematic design.

No self-respecting hang glider designer would think twice about adding tail surfaces (picture source).
A third way of avoiding a conventional tail is the V-tail, which was invented in 1930 by the Polish engineer Jerzy Rudlicki.

Ultraflight Lazard ultralight with inverted V-tail (picture source)

In the 1940s and 1950s, roll, pitch and yaw control was demonstrated through variable wing geometry, the aim being to eliminate the drag and normally negative lift of the tail.
When variable geometry wings were re-invented in the 1960s, the original purpose had been forgotten or discounted, and variable geometry was restricted to matching the wing's characteristics to different speed flight regimes, pitch and yaw control being performed by conventional tail surfaces.
As they had both the weight of wing hinges and actuators and the disadvantages of tail control surfaces, they were probably the worst of both worlds.
The experiments were restricted to remote controlled prototypes, to prove the principle before developing manned aircraft (their designer was distressed by the loss of life from some earlier inventions). Apparently, money issues and politics stopped further development at the time in the UK, though this page suggests Nasa studied the idea, finding some difficulties including unexpected drag. Whether those difficulties could be solved now ... I've no idea. I'm no expert, just an observer, so I'd be interested to hear any more about these ideas.
Pity, the Swallow (source here) would have been a nice looking machine.

Sources: Life of Barnes Wallis


text:
What are the maximum altitude and speed of a GT500 ultralight?
What are the maximum altitude and airspeed of a GT500 ultralight?

All the information is in the Wikipedia article in the original post.  12,500ft,   90kts

The service ceiling is 12,500 Feet MSL (Exactly 3,810 Meters), and the never exceed speed is 103 MPH (About 89.5 Knots).
Source 1: http://www.air-techinc.com/ultralight_aircraft_details.php?ptid=118
Source 2: https://en.m.wikipedia.org/wiki/Quicksilver_GT500#Specifications_.28GT500.29


text:
What is a Cessna 172's maximum altitude?
What is the maximum altitude at which a Cessna 172 can fly?

The absolute ceiling, or the maximum height an aircraft can fly to, is usually not published; manufacturers usually use service ceiling as the benchmark.  Service ceiling is the maximum altitude which the aircraft can attain flying in air at Standard Temperature and Pressure (29.92" Hg and 15° C at MSL) and still be able to climb at a rate of at least 100 feet/min.
Depending on the model 172, this is between 13,000-15,000 feet ASL.  A Cessna 172SP has a published service ceiling of 14,000 feet ASL.

Again whether an airplane can attain these altitudes on any given day is dependent on the condition of the air.  The aircraft may be able to ascend higher than this on days when the air is very cold and there is a high local barometric pressure or lower on days when the air is warm and/or at a low barometric pressure in the region.

18,300 feet in a Cessna 150

Well again, the pilot of that 150 never hit an absolute altitude as the story states that he was still able to climb at 100 feet/min at that altitude.  In addition you have to have data on the ambient atmospherics on that flight in order to draw any data from it.

Absolutely, I just posted the story to back up your claim that it is the service ceiling, not maximum altitude.

In September of 2007 in my 0-360 1959 172  I attained 18,003 ft GPS above 19AZ. I checked with Cessna customer service. The fella called me back a couple of days later. As far as he could find I did set a record. The plane was still climbing slowly and rather wobbly. I was happy to roll out and level off at 15 000 ft where I could catch my breath. I took off with a little less than half gas.
This is an addendum to my earlier post setting the 18,003 ft. GPS altitude record for my 1959 Cessna O360 172 in September 2007.
How could it be " impossible "? I was there. My GPS was pretty accurate. In fact, I held my holding pattern for a couple of minutes to get the average GPS altitude. I was carrying a carbon fiber Pulse Ox O2 tank but didn't feel the need to turn it on. I have experience with high altitude hiking and mountaineering, so sitting in a little airplane, pressure breathing was an easy task. It was the wobbly or sloppy control surfaces I was concerned about. There was little to no wind that afternoon, but even so, the Downwind Leg added to slop. My take off airport 19AZ elevation was 3,370ft and the ambient surface temperature was about 90°F. I was in constant radio contact with my wife and a neighbor who were way down below. Early on in my flight training I mastered an Unusual Attitudes and Emergency Maneuvers course. Subsequently I was offered the Extra 300 that was available on the school's flight line for rental. So with a little calculated planning and careful preparation I felt confident that day. Lawrence Allen PP L&S airlarone@gmail.com

Based upon my first hand experience in a C-172M, which got to 17,500 (what a chore!), I would believe you could have a record.  Remember that a lighter aircraft will likely get higher.

I've been above 17,000 in a C-152 but there may have been some mild wave lift present.

I hope you had O2!

You are seriously suggesting that the control surfaces were "sloppier" when flying downwind than when flying upwind?  Perhaps you should have turned on that O2 to increase mental acuity--

According to this, the 172's absolute ceiling (the altitude above which it is impossible to fly under standard meteorological conditions) is 15,000 feet.

According to the C172M manual, the service ceiling is 13,100ft:


text:
Why aren't the undersides of military aircraft painted bluey-grey to camouflage them against the sky?
Why aren't military aircraft painted a bluey-grey colour to camouflage them against a bluey-grey sky?
(I researched this but couldn't find a clear answer)

Related, possibly even a dupe

I believe that you're asking from a false premise. You might be better off asking the inverse question: Why are these specific aircraft (with images/links) not painted blue-grey

Also related, though not a duplicate: Blending in isn't always the best camouflage option.

The B2 stealth bomber is not only painted on the bottom to match the color of the sky it flies in, but for some missions actually adjusts its altitude to find the least visible level of lighting.

Shades of Blue-grey you say? So.......
The F15

(source: boeing.com)
The Mig21

The AWACS

(source: airforce-technology.com)
The Eurofighter

(source: ausairpower.net)
To name a few I could think of from the top of my head. Almost every military aircraft has a variant that has been painted along the blue-grey spectrum at some point or another.

The next question could be why is the AWACS radar dome black with a white stripe...

Psy-ops against the population on the ground who can't see the camouflaged plane so freak out at the flying saucer. *nodnod*

You probably only think there aren't any because the ones we see, typically, are for show. Say, for example, the blue angels, or for domestic use where camouflage isn't as important. In a foreign theater of war, the aircraft would be painted appropriately I.E. blue-gray, black (depending on the mission).


text:
Would a wireless fly by wire system be practical?
Given that most modern aircraft are controlled using the fly by wire system, what is the likelihood or the drawbacks of transmitting those fly by wire instructions from the cockpit and or cockpit computer wirelessly? Wires add weight to the aircraft and hence increase the net fuel burn. I'm assuming a totally wireless system is not already in use today.

and risk loss of communication?

A fly-by-wireless then...? The question is not so clear, because wireless sensors, wireless feedback, and wireless avionics are already in sight. Do you mean wireless control of actuators? Note: Control of actuators doesn't account so much in wire weight, especially when hydraulics powered actuators are used. But the ratio will increase in "more electric" aircraft.

There's a short paper from NASA on this subject: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20070013704.pdf

I tried but failed to find the User Friendly cartoon where passengers take control of the plane with their laptop wifi...

I think you've overlooked something: most if not all of those devices will still require wires in order to provide power.  If the weight and/or cost of separate control wires is an issue, it's certainly possible to multiplex the data & control signals over the power wires.

A very detailed inventory of WAIC on the ITU site (Report M.2283): Technical characteristics and spectrum requirements of Wireless Avionics Intra-Communications systems to support their safe operation

There are reseach projects underway close to this area, one example is SHAWN > https://scc.rhul.ac.uk/research-projects/

The fly-by-wire is absolutely vital for control of the aircraft, and the three dominating factors here are safety, safety and safety. Weight is not one of them. The fly-by-wire system is triple or quad redundant: instead of removing a set of cables, the manufacturers are installing 3 more cable looms, just to make sure that the system always works.

Wires are safer than wireless!. There are active transmitters and receivers in wireless systems, which can fail. Signal reception depends on the quality of the space between transmitter & receiver: can the signal always penetrate the aluminium bulkhead? What happens to the wireless signal when flying past airport radar or in the weather radar field of another aircraft?
Shielded wires are passive and relatively immune to electro-magnetic radiation, and are the means of choice for such a safety critical system.

Update
The OP was on fly-by-wire. In a sense, the flight control system is the most safety critical system on board and must be immediately available at all times. The presentation linked to by @mins in a comment reports on the progress of on-board wireless communication, for systems with a less critical safety aspect:

Examples of Potential WAIC Applications

Low Data Rate, Interior Applications (LI):

Sensors: Cabin Pressure - Smoke Detection - Fuel Tank/Line – Proximity Temperature - EMI Incident Detection - Structural Health Monitoring - Humidity/Corrosion Detection
Controls: Emergency Lighting - Cabin Functions

Low Data Rate, Outside Applications (LO):

Sensors: Ice Detection - Landing Gear Position Feedback - Brake Temperature - Tire Pressure - Wheel Speed - Steering Feedback - Flight Controls Position Feedback - Door Sensors Engine Sensors - Structural Sensors

High Data Rate, Interior Applications (HI):

Sensors: Air Data - Engine Prognostic - Flight Deck/Cabin Crew
    Images/Video
Comm.: Avionics Communications Bus - FADEC Aircraft Interface - Flight Deck/Cabin Crew Audio / Video (safety-related)

High Data Rate, Outside Applications (HO):

Sensors: Structural Health Monitoring
Controls: Active Vibration Control

From the same presentation: An A380 has 5,700 kg of wires on board, and 30% of them are potential candidates for a wireless substitute. So wireless communication on board of aircraft does make sense, starting with the non-safety critical systems first.

"Wires are safer than wireless", until they are broken. Wire + wireless may be safer (page 10) than 2 wires.

@mins Yes everything can break. Does one have a higher chance of breakage than the other, is the question. Wireless does not even have to break to be rendered inoperative by external radiation.

@mins Flight control cables can break, hydraulic lines can break, the electrical wires carrying power to the actuators can break, etc.  If the wire with the signal to the actuator breaks, is the wire with the power for the actuator still there?  Sounds like the solution would be redundant & physically separated sets of control and power wires, rather than a jammable wireless control that still needs power at the actuator.

@RalphJ: What the presentation linked explains is that when all redundant wires have no other possibility than being close together (e.g. in the wing), wireless offers another choice ("Route segregation, combined with redundant radio links, provides dissimilar redundancy and mitigates risk of single points of failure". The key point is this is a mix wire+wireless, not wireless alone. And of course it's not for power, but for weak signals.

System failure aside, a wireless system would be incredibly trivial to jam.

"incredibly trivial to jam": Not from the inside of a Faraday cage, should the communication occurs outside of the cage. That would indeed be the case.

@mins what makes you think the jammer would not be inside the cage...

Lightning is another thing that comes to mind....

What @reirab said.  If you can control your aircraft wirelessly, so can someone else.  Or at least, they can certainly block your ability to control the craft.  Which for a malicious actor is all they really need to do.  And no, an aircraft is not an effective Faraday cage.  If it was, you wouldn't get so many people yakking away on their cell phones the moment the plane touches down.

@mins Yeah, aroth is right. Aircraft aren't that great of Faraday cages. There's enough attenuation that GPS signals don't work well (since those signals are barely above the background noise anyway,) but not enough to even significantly affect a cell phone, let alone a jammer. For that matter, I've connected to the Wi-Fi in a lounge from inside a plane sitting at the gate a few times before. Also, the avionics would be inside the fuselage, too, though the flight control surfaces are obviously outside it.

@aroth: Aircraft wireless is moving on, as I wrote at the top of this page, wireless sensors, wireless feedback, and wireless avionics are already in sight. I didn't mention rudder or ailerons actuation. A band has been secured by the WRC/ITU (4/5 GHz that is today used for radio-altimeters, but will be vacated). Indeed there are challenges, but industry is already spending money on tests, regulation and standards. The big driver is sensors are gong to be in astronomic quantities in future aircraft, and wires can't be used.

@reirab: Yes windows offer this possibility, but windows can also be made to stop the 4/5 GHz band if needed. Then please also consider that wire jamming is also possible (this is the official reason behind turning off PED), but jamming devices can also be detected and neutralized easily.

@mins Sensors, feedback and avionics are one thing, and may not be bad. Parts that make the airplane go different places are entirely different. Wireless is incredibly trivial to interfere with. Lnafziger is absolutely on the right track. Lightning is worrisome. Also, if you add in the needed encryption + validity and redundancy checks, I'd imagine the latency of a wireless signal will be significantly greater than a wire. Even a tiny fraction of a second is more latency than I want. I'd be less comfortable with a fly-by-wireless aircraft than with a remote-controlled, pilotless aircraft.

RE your update, yes but as I pointed out in my answer, you can so the same with single wire communication and distributed controllers/computers without all the issues and risks of radio communication. A method the naval industry has been using for a couple of decades to reduce the millions of feet of cables that needed to be run through modern warships.

Your addition on WAIC shows the major revolution that is happening in aerospace regarding wires. There are 2 very detailed documents for those who are interested in details: ITU report M.2283, and this full presentation used in 2015 for a workshop (the first was an extract only).

That will be very unlikely simply because wireless is much less reliable by several order of magnitude.
considering the current day an age of terror threats if the encryption (and you will need encryption) is ever compromised this would allow a passenger to hack into the datastream and Man in the Middle the controls for a hijack without ever entering the cockpit.
You also have not considered the power requirement of the wireless communication, that will also increase fuel cost.
To save a few hundred kilograms of weight this is never going to happen.

Never going to happen? Well the goal of the AVSI is to save 30% of the wire weight using radio ("About 30% of electrical wires are potential candidates for a wireless substitute!").

@mins that presentation doesn't aim to replace the aviation control wires, (which is what the question is about)

Just thoroughly jamming the signal would be enough -- hacking to take control would be "nice" from an attacker's standpoint, but jamming the frequency and thus all the controls would be entirely sufficient to bring down the aircraft.

No need to crack the encryption. A jammer would take down a "fly-by-wireless" system with ease and they're pretty trivial to make. Just broadcast a bunch of white noise in the right band and that's it.

Quantum entanglement may be unhackable and unbreakable. I would define it as wireless.

@ChristiaanWesterbeek : unless its software implementation has bugs. Practically uncrackable encryption already exists (which would need billions of years to brute-force even if every atom in the universe was a computer), but they do occasionally get hacked due to bugs in their implementation.

The problem is not that encryption could get hacked, but that the control center could be hacked. Is it easier for 500 people to storm an aircraft in the air and break into the cockpit, or to storm a control room running servers on the ground that send commands remotely?

@reirab You can design a wireless protocol to be nearly immune to jamming attacks if it's heavily spread-spectrum. The term for this is LPI (Low Probability of Interception). You can use FHSS+DSSS with OFDM and frequency hopping. These are all common technologies used to reduce interference, but can be easily modified for anti-jamming purposes. Sending out an ultra wide-band white noise generator would use an obscene amount of power (an impractical amount).

Although technically feasible, having wireless communication between cockpit and the various end-points around the aircraft produces significant issues.
Primarily:

Channels: Unless you use multiple frequencies, each sensor or driver would need it's own radio channel. Add in redundancy and you need like three channels per sensor or actuator station.
Bandwidth: Wireless communication is limited in how much data you can transfer at a time. Since you would be sharing the channels over multiple devices, this further limits how fast you can communicate with it.
Interferance: Assuming you can even get all these devices working at the same time, you are very susceptible to electrical noise. Whether that be Timmy using his little game-boy, or dad using his electric razor in the washroom, or travelling through an electrical storm, a sudden loss of communications in any form would be detrimental to the passenger and crews flight experience.
Security, Hacking / Blocking: It would be rather too easy for a would be terrorist to turn on a transmitter to block the wifi or hi-jack the control system.

As such, wireless communication would be a rather dangerous road to venture down.
As for harnesses. When it comes to control systems, harnesses can be significantly reduced by using a different method. By using distributed smart controllers located around the aircraft, a single wire communication system can be used to connect them to the main flight computers. That is, you really don't need a wire in a harness for every switch in the cockpit.
As always, there needs to be redundancy here, you design it with two or three communication cables routed through the roof, floor etc. for redundancy in case one fails or is severed. You would still need a power distribution system of course.
However, the issue with all these methods is that of channelling too many functions through a single point. Although it may be a simpler system and more reliable, the consequences of a failure are far more significant.

What do you mean with "unless you use multiple frequ., each [...] own radio channel"? Classic radio channels actually use multiple frequencies. Mind you that today we can choose from many other multiple access techniques including time division and spread spectrum. Likewise, wireless bandwidth may be very high. There is really no shortage in terms of channels and bandwidth for the requirements of flight controls.

@bogl yes bandwidth and channels go hand in hand here. You either use a lot of channels with limited time division or less channels and a lot of time division. Either way,, it's problematic for real time control.

Do you really need a different channel for every item?  Similarly to how you can have multiple transmitters on a bus, or multiple cell phones on the same frequency, you don't need a different channel for each transmitter.  You can use time multiplexing, code-division multiplexing, or even space-time coding if you're ambitious,   I'm not sure how deterministic real-time behavior can be guaranteed for these, but real-time wireless networks do exist.

@CodyP as I said in my comment. It is a balance.

No.
While wireless communication could help to reduce the number of cables, the remote control units and remote terminals still require cabling for power.
Advantages of wireless systems include mobility and flexibility. These could be driving factors for some early prototypes, but clearly not for certified airliners. The side effect of harness reduction is not significant.
Thus, doing with less wires is possible, but wireless is not.

A really excellent point!

In my opinion, the most important issue would be that of immunity towards the interference to wireless signals (from the FCS to the actuators) from external sources or impact of environmental factors on the transmission of the signals - what is the reliability of the wireless signal transmission in all the imaginable situations. Until we have a technology which eliminates these issues the industry would be very sceptical of use of wireless FCS. As of today, the next thing coming up in FCS is Fly-by-Light i.e. signal transmission using fibre optics. There are a number of pros of FBL over conventional FBW such as high speed, immunity to EM interference etc, but at the same time it may not be significantly lighters than copper wires as a over-all system which could trigger the switch to FBL in civil domain for example.

Fibre optics is indeed a good and relatively immune way of point-to-point communication. The trouble with it though is that it is difficult to implement in a databus setup, hard to splice a signal into an existing wire. Hub-and-spoke architectures grow exponentially with number of sensors, and there are more & more in modern aircraft.

Fiberoptics also tend to have the problem that they don't deal very well with being jerked about. This isn't really much of a problem on the ground, but in an aircraft that can be subjected to fairly strong turbulence, that's an issue that you need to keep in mind. Admittedly, it can be overcome, but by that point one has to start asking what you're gaining by using fiberoptics over copper in the first place. Also, as long as the computers are electronic, don't forget that at some point you'll have to have some kind of device bridging the electrical/light gap, at best introducing only latency.

There are several pros and cons to the system, and several great links to existing research have been provided by others here. Manufacturers like Gulfstream and Boeing have prototyped some examples of wireless avionics and it's an area of active research with plenty of papers proposing different strategies.  So I wouldn't go so far as to say that fly-by-wireless is unworkable or a horrible idea, although it's telling that it hasn't been widely deployed yet in other industries for in-vehicle networks to my knowledge. Like many ideas posted here, it has its merits but the benefits may not be enough to overcome the challenges.
Pros to wireless control:

Less cabling weight, maybe by as much as over a thousand kilograms
Reduced engineering cost for harness design, cable routing, and shielding
No wires that you have to shield from electrical interference (instead you have an antenna picking up interference)
Fewer issues due to broken connectors, snapped wires, transmission line effects from faulty terminations, etc.

Cons:

Increased engineering cost in wireless transmitters
Increased complexity (think of how Wi-Fi has more connection issues than LAN)
Greater chance of single-point-of-failure issues.   Aircraft have several redundant buses routed through different points in the aircraft. It's easier to jam or take out all wireless communications than all these redundant wires.
You need to use a secure architecture with encryption and authentication signatures because you no longer have a guarantee that intruders aren't on the data bus.  The military already uses similar technology in a variety of radio applications.
Extra security software and hardware to detect network intruders, prevent dangerous interference, etc.
Impossible to completely protect from jamming, even if using military-grade anti-jamming techniques like spread spectrum and frequency hopping.

As an interesting point related to hacking, most modern flight control computers are immune to nasty Byzantine General errors.  These errors are situations where one of several sensors or control computers fails and misleads the others, including even lying to one and telling the truth to another.  Even in these situations, the system is designed to detect the liar and still reach full and correct agreement between the functioning computers.  To take down these systems you'd have to impersonate two, or sometimes even three, flight control computers or servos at once.
Also, many systems are designed to prevent hardover.  For example, the  if the rudder is detected to deflect fully, the avionics might revert to a simpler backup control system (which is possibly mechanical).  These systems can be circumvented with the right techniques of course, but to imply that its trivial for one system to go rogue and take down the whole plane is like implying a bridge will fail if you cut one support beam.  You shouldn't ignore the extensive safety analysis and redundancy that goes into these designs.

The expression fly-by-wire is reserved for the flight controls, to distinguish them from fly-by-cable, just mechanically deflecting a valve or the control surface directly. There is research budget spent on wireless technology for aircraft, for systems with low safety impact. Not the flying controls.

@Koyovis If you read the Gulfstream link I posted, it talks about a prototype with "application of wireless signaling for a primary flight-control surface".  So it appears there is research on wireless technology for flying controls.

" A mechanical system controlled the ailerons; a Fly-By-Wire system manipulated the outboard spoilers; the Fly-By-Wireless system handled the mid-spoilers; and a fiber-optic Fly-By-Light system moved the inboard spoilers." Interesting research. Primary control still done mechanically.

Wires are far more resistant to electromagnetic interference, either intentional or situational, than radio signals.
Also, transmitting radio signals to remote receivers that are encased in either aluminum or carbon fiber would pose some difficulties. One could use the aluminum skin of the aircraft as an antenna, but that would be supplying a great antenna for external radio signals, too, and you have a potential interference issue again, one that could be applied external to the aircraft.
A more practical approach has been to replace metal wires with fiber optics. Fiber optics have a higher speed and much wider bandwidth that can carry multiple signals per strand, as well as weighing a lot less.
Some years ago, the Lockheed C130 was redesigned with a fiber optic based system. The result removed so much wire and weight from the cockpit area that the previously optional cockpit armor became standard, to keep the plane in balance when it had no cargo.

Something I haven't seen any other answer touch on is this: Wireless transmitters require wires to power them. Instead of running a wire from cockpit to system, you're running a wire from the planes power grid to the transmitter, then another wire to the receiver.
Congratulations, by not using wires, you've doubled the number of wires.

The wired transceiver would have also required power.  Assuming 2 signal, power, and ground, you halve the number of wires.  But power may be routed differently than data.

The goal is not to reduce the number of wires, but their length/weight. And most wireless devices won't need to be powered from the aircraft, that's the element which allows to move on. Devices can have batteries or other sources of energy like induction on RFID.

@mins How long are these batteries going to last? How will you replace them when they're low? How much of a weight savings do you expect to gain when you're adding all these batteries? How do sensitive avionics in the aircraft deal with the entire airframe being bathed in magnetic flux from induction chargers?

@UIDAlexD: "How will you replace them when they're low?" The batteries on my home smoke detectors last 10 year and that's not rocket science. Many solutions exist. E.g. I'll have a single battery for 50 sensors and I'll charge it during maintenance, on the ground. If I use an induction method, the inductor will stay on the ground.

Except in the rare cases of two-wire passive sensors, or one-wire signaling for hydraulic acutators most flight control computers, servos, and actuators already have power going to them, so you haven't "doubled the number of wires".


text:
What are the procedures to get a revoked mechanics certificate reinstated?
At one point I held a mechanic's certificate. However due to poor judgement it(the certificate) was revoked due to a narcotics conviction.
How can I get it reinstated? Is there refresher classes?

I think you've to apply for a certificate again after the required period and take the tests again. From 14 CFR §65.11 Application and issue:

(d) Unless the order of revocation provides otherwise—
(2) A person whose mechanic or repairman certificate is revoked may not apply for either of those kinds of certificates for 1 year after the date of revocation.

In your case, you have to wait for 1 year after the final conviction to apply. From 14 CFR §65.12 Offenses involving alcohol or drugs:

(a) A conviction for the violation of any Federal or state statute relating to the growing, processing, manufacture, sale, disposition, possession, transportation, or importation of narcotic drugs, marihuana, or depressant or stimulant drugs or substances is grounds for—
(1) Denial of an application for any certificate or rating issued under this part for a period of up to 1 year after the date of final conviction;

I think that taken together, the above means until 1 year after the revocation or conviction, whichever is later.

In addition to the articles listed above, you must first seek out an Approved (SAP) substance abuse professional to administer “treatment/punishment” then submit to supervised drug screens for a determined period of time thereafter, which is decided based on individual case stipulations and risk factors of repeated offenses until the time period determined has expired then you may reapply and retake all tests including oral and practical examinations in addition to the three written. Plus you may have to pay additional fees and penalties for the infraction in addition to the fees for the tests and the test administrators.

Can you cite some sources please?  This looks like a good answer in the works but it could definitely be stronger by adding a few sources.


text:
Do different types of missiles indicate different lock tones to the pilot?
Are there different lock tones for different types of missiles, e.g. air-to-ground (AGM) or anti-ship (AShM)? If so, what information do the tones give the pilot? Are they a way for the pilot to know which type of missile is selected?

Your question about weaponry appears off-topic on this site about aviation.

The question is not about weaponry, but about in-cockpit weapons avionics.

@CGCampbell In cockpit weapon avionics are still off topic because they have to do with the weapons, not with flying the plane (IMHO).

Military Aviation is part of Aviation, and this is absolutely about military aviation. Voting to reopen.

@JayCarr IMHO, I disagree here. Cockpit weapons avionics, and especially the audio component used that is the question here, is wholly and completely about flying the plane and killing the Bad Guys while not crashing yourself.

@CGCampbell hmmmm, perhaps you have a point.  We've always had a hazy line between military topics (off topic) and military aviation topics (on topic as Ralph J correctly states).  This seems to hover right on the line.....   With your logic though, I'd agree the question should stay open.

Lock tones are normally used for (surface/air)-to-air infrared homing missiles. Air-to-surface missiles don't "growl".
The tone is used to indicate missile readiness and quality of lock, not the type. Phantom pilots in Vietnam used to cycle between all available Sidewinders to check which seeker had the best tone then put the worst one to be last in the firing order (source: "Sierra Hotel : flying Air Force fighters in the decade after Vietnam" book, page 12)
At first there was a volt-meter in the cockpit to do that, but during development testing they figured out looking inside the cockpit in a dogfight to check if the missile is ready to fire wasn't a good idea, hence the tone frequency was introduced (source: Fox Two).


text:
What are the extra wheels for on the Harrier series?
On the Harrier series, what are the landing gears on the end of its wings for?


text:
Where do I place pressure ports on an airfoil?
What are the criteria for placing pressure ports, i.e. is there any procedure for determining where to locate them? I have a NACA 0012 airfoil with a chord length of 150mm and I want to add pressure ports to it. How should I proceed?

Depends on what you want to measure.
Normally, pressure ports are bunched close to the leading edge to give sufficient resolution of the steep pressure gradients (which result from the high local curvature). So scale the local pressure port distance with local curvature.
But maybe you want to have a high resolution of the beginning flow separation near the trailing edge? Then you need to place the pressure ports close to the trailing edge.
Or maybe you want to study the laminar to turbulent boundary layer transition at mid-chord? Then any pressure ports in the laminar region will cause a local transition and show a 15° cone of turbulent flow which will mess up all other measurement behind them. Now you need to restrict the number of ports in the forward part of the airfoil and need to give them enough lateral separation to get what you want.

At first, I thought the question was asking the best place for a static port on a wing.. ;)


text:
Is the airspace at KGPT class E or G when the tower is closed?
I'm a bit new to airspace and I'm trying to figure out if the airspace around Gulfport-Biloxi International (KGPT) changes to class G or E when the tower closes.  Looking at KGPT's airspace on a sectional, it is Class D with a note to check NOTAMs/Supplement for Class D/E (sfc) effective hrs.

I've checked the chart supplements and it says Class G when the tower is closed, but the AIM leads me to think it would be Class E at 700' MSL (with Class E extensions changing to Class G) when the tower is closed since it has ASOS.  Does this sound right, or am I missing something?

Related answer to a related question  -- https://aviation.stackexchange.com/questions/54048/what-class-is-the-airspace-at-kgcn-when-the-tower-is-closed/75377#75377

To expand a little more on what @rbp said, the VFR Sectional Note is referring to the Class D and Class E (sfc) designations.  So, when referring the the Chart Supplement, which says AIRSPACE: CLASS D svc (1200-0500Z) other times CLASS G they are referring to the Class D and Class E (sfc) specifically—just as @rbp said.
Now consider what the next level of controlled airspace is when the tower is closed and the airspace over KGPT becomes Class G. It would be 700’ AGL Class E airspace. The AIM goes on to detail this (emphasis mine):

Where a Class D surface area is part-time, the airspace may revert to either a Class E surface area (see paragraph 3−2−6e1) or Class G airspace. When a part–time Class D surface area changes to Class G, the surface area becomes Class G airspace up to, but not including, the overlying controlled airspace.

Source: Aeronautical Information Manual (AIM), Change 1, May 26 2016, 3-2-5 Class D Airspace (13 MB PDF)
And goes on to explain in Note 2 of paragraph 3-2-5 (with added emphasis):

Normally, the overlying controlled airspace is the Class E transition area airspace that begins at either 700 feet AGL (charted as magenta vignette) or 1200 feet AGL (charted as blue vignette). This may be determined by consulting the applicable VFR Sectional or Terminal Area Charts.

If the chart says its Class G when the tower is closed, they are talking about the surface area ("sfc" in the note), not the overlying airspace.

authors: پارسا کشاورزپور


text:
Is there a viable alternative to liquid hydrogen as a fuel for scramjets?
Given the difficulty and complexities of storing liquid hydrogen for commercial flight and the high velocity of air passing through  a scramjet, do other types of fuel provide a feasible alternative or solution for scramjets to achieve their maximum theoretical speed of Mach 24? are there any better alternatives?

Could you narrow down your question on a fuel type? I guess you are talking about liquid fluid? Rocket-motors might use hydrogen or even  kerosene. Scramjets also use a wide spectrum of fuels. Or are you talking about hypergolic fuels?

"High energy fuel" might be more about what you are trying to ask.

Not sure what you are asking here. What do you mean by "rocket fuel"? Liquid hydrogen? You propose it as an "alternative "  what do you think current scramjets are using as fuel? Can you provide more context or background on what you are trying to get at?

If your idea is to boost the power of a scramjet by using rocket fuel, then you'd have to include the oxidizer that all rocket fuel has. In that case, you wouldn't have a scramjet, which is an air breathing engine. You'd have a rocket.

To list possible alternatives, it is helpful to know why hydrogen is used for scramjets today. The key is the speed of propagation of a combustion in the hydrogen-oxygen mixture.
In order for combustion to take place, the fuel needs to mix with the air and then the ignition needs to propagate fast enough through that mixture in order to allow the combustion to stay stationary relative to the engine. Combustion which happens after the fuel-air mixture has exited the nozzle of the engine is not helping in propulsion.
Therefore, to be suitable as a scramjet fuel, the candidate has to

mix with air really quickly,
have a flame front speed higher than the flow speed in the scramjet, and
achieve complete combustion as quickly as possible.

In all points hydrogen is hard to beat. It is so good that scramjet designers have decided to accept it as their favorite fuel despite of all its disadvantages, which are well known:

Low volumetric efficiency, even in liquid form.
Storage in a cryogenic or high pressure tank.
Small molecular size, so it diffuses into and leaks through many materials, even metals.

All bullet points can more or less directly be traced back to the small size of the hydrogen molecule. Any other scramjet candidate would also benefit from a small molecular size, and acetylene would be the next best candidate, with a flame front speed of 168 cm/s at room temperature (compared to the 364 cm/s of hydrogen).
The difference in speed makes clear that no other fuel comes close to hydrogen.

Kampf How can flamefront ( 364cm/s) speed more than flow speed? That speed is 0.1 speed of sound. And speed of flow in scramjet is supersonic.

@Auberron You're right, but this value is for room temperature. Due to the high compression, gas temperature in a scramjet is around 1000 K, and then the flame speed is sufficiently high if flame holders are provided.


text:
Is the entire length of a B747 or A380 wing used as a fuel tank?
It is generally understood that the fuel tanks of aircraft are in the wings, but specifically, is the entire length of the the wing of:

an Airbus A380 Jumbo used as fuel tank?
a Boeing 747-800 Jumbo used as fuel tank?

What percentage of the wing length is used as a fuel tank and for what reasons, for:

an Airbus A380 Jumbo
a Boeing 747-800 Jumbo

If you do a Google search for "A380 fuel tanks", things like this image pop up in the results.

Fuel tanks take most of the space in aircraft wings, but not all. There are other things on wings too. They are ailerons, flaps, slats, air brakes. On most airliners, the engines are attached to the wings too, so their assembly takes up space.
On the two aircraft of your interest, here are the pictures:
A380 (its nickname is not jumbo, but superjumbo)

Image Source
747

Image Source

So that "center wing box" in the A380 does not hold any fuel?

@Bergi AFAIK, A380s don't have a center wing tank (CWT), unlike most other widebodies (both Airbus and Boeing).

Also, note that these images do not show the critical "dry bay" sections above the engines that are devoid of fuel tankage.  These minimize the chance that projected parts from an engine failure will pierce a fuel tank and cause mass leakage onto a hot engine, leading to an uncontrollable, fuel-fed fire.

Your question regarding how much length of the wing is filled with fuel has been answered well. If you are wondering how the location of the front and back walls of the fuel tank are determined and designed, here is the answer:
The existing wing structure of front and rear spars and upper and lower wing skins act as an integral wing fuel tank. When the wing is assembled sealant is applied between all parts to make the wing water-tight.
Integral wing tanks are primed with special yellow paint which acts as a barrier against the fuel to protect the aluminum structure.
Perfectly sealing the inside of the wing is very important. There are many Quality Assurance inspections and a final leak test.
The composite fixed leading edge and fixed trailing edge which complete the forward and aft section of the wing structure and contain the flight controls are attached to the front spar and rear spar respectively.
An airliner wing will have a "dry bay" just over the engine strut/pylon for safety in the event the engine were to experience a catastrophic failure where compressor or turbine blades were thrown into the wing tank.
On a 777 the Dry bay area is blocked out by a composite piece that is secured and sealed in place. Each wing will usually have one dividing wall in it in the vicinity of the engine pylon (everything inboard from that point is considered the center wing tank, including the center wing section/tank).
Airliners with 4 engines will have each wing divided into at least 2 sections (one to feed each engine). As you can see in the illustration in a previous reply, the 747-400 has 3 tanks per wing plus the little surge/vent tank at the very end.
The end of the wingtip will have a vent area where expanding fuel vapors can escape (and may be called a "surge tank"). Look for the little NACA intake duct on the underside of the wing, which also brings air in to replace the fuel that is being used by the engines so that the fuel can flow freely out of the wing without suction being created.
On modern airplanes especially (like the 777 and later) the very extreme end of the wing (beyond the surge tank) is not very substantial in construction (made of very thin material) and is therefore not used to store fuel.
The raked wingtips of the 767-400, 777-200 LR, 777-300 ER and 747-8 are extra extensions added on to the end of where the "official" wing box structure ends. These of course do not contain fuel because they are a very light, thin composite structure just strong enough to take aerodynamic loads.


text:
What are the particular challenges faced when landing at Bristol airport (UK)?
Earlier this year I returned to Bristol on flight TOM-6633, and like most landings at Bristol the passengers found the experience physically immersive, attention grabbing, and at least a little exciting - enough for the odd gasp and finally some small amount of scattered cheers and claps.
In layman's terms - the approach was characterised by the plane apparently hitting a very large number of considerable bumps, while wagging the wings up and down/rolling from side to side all the way in (trying to avoid the bumps, maybe?). Finally we got near the tarmac and the plane touched down "decisively", enough to make all aboard thankful for buttock fat.
So what are the particular challenges typically facing a pilot coming into Bristol (UK) airport?
Are these challenges considered fun by those folks in the front seats with the fancy hats and scrambled egg (ie: Pilots)?

Sounds like there were probably strong wind gusts. Look on YouTube for “crosswind landings” and you’ll see lots of aircraft rolling and pitching to deal with the wind. A firm touchdown is preferable in those conditions.

Some turbulence you say?  https://i.redditmedia.com/DNg5H60VItnt-A-sVFgUCD52HqqGp4_MgGRqJAby3co.jpg?w=548&s=2c5242eab2d0ccee3287497b947449fc

I have flown into Bristol quite a lot, as I live near there. Most landings are boring, but with good views on a clear day.  Most landings are also from the east, on 27 as the prevailing wind is from the west.
On the fairly rare occasions when you come in from the west on 09 it tends to be in unsettled weather, as that correlates with easterly winds.  You're also coming in over the Bristol Channel (not renowned for good weather, at least at sea level). Final approach from both directions is over some low but lumpy hills, more noticeable to the west of the airport.
"Earlier this year" written in April suggests late winter/early spring, when we had some interesting weather brought in from the NE. With the exact date it might be possible to narrow things down.
Overall it's nothing special but it's perfectly possible for a few things to come together to make it more interesting.

FWIW, I looked at the airport on Google Earth. The runway sits at around 600 feet. I then ran the pointer around the airport at roughly a mile away from it and saw all elevations less than the runway. Thus it would appear that the airport sits on the top of a bit of a hill. My experience has been that hilltop runways are naturally more turbulent in high wind than those not on a hilltop.

@Terry that seems right.  The nearest noticeably higher point is Dundry hill and that's about 2.5 miles ENE

Nothing, really. It's just another airport. The runway has normal dimensions, there is no high terrain around, the approach procedures are completely standard.
Depending on the weather, you will get some turbulence anywhere in the world. That has nothing to do with being in Bristol.


text:
Where to find a 1983 NTSB report of a R-22 clutch failure?
Why can't I find the incident report I had to file after my death defying landing at John Wayne Airport in Costa Mesa Ca. around 1983?
They found the clutch with 4 belts to have malfunctioned and grounded all Robinsons in service, until a better configuration was developed.

Where have you looked? The report is probably not digitized you may have to request a copy from the NTSB.

Yeah, it looks like you'll have to poke the Records Management folks at the NTSB when they get back in on Tuesday :) See if you can get as much detail as you can in the meantime -- the incident report form is also called a 6120.1 if that helps.

Thanks, Yes I Have looked through NTSB , also through some FAA links..

Not the incident you refer to, but an interesting review of more recent R22 clutch belt failures is found in this Australian report

I don't think your "death-defying experience" was classified as an incident or accident. Checking the list of occurrences the NTSB classifies as an incident does not show that what happened to you needs to be reported as one. Mechanical failures of all kinds happen on aircraft all the time. Very few of them are required to be reported to the NTSB.

Well they grounded all Robinsons Worldwide and went from the 4 belt setup to 1. In my case 3 had broken and wrapped around the main shaft of the rotor, and the clutch was still stretching the last 1. So honestly I don't know how it was reported. Death defying probably not.tons of smoke ,yes,. Just happy to be here.

Mechanical issue, likely reported to the FAA and to the manufacturer, but not to the NTSB. Good outcome. :)

Thanks. Mostly luck the ground was there at the right time. Frank Robinson came out to view it himself, and I may have pictures somewhere.


text:
Do you need a commercial rating for aerial application work?
So to be qualified to do aerial application work do you have to have a private license with a commercial rating?

What is "arial application"?

Crop dusting. Spreading chemicals on fields by air

Short answer: you can do aerial application on your own crops with a private certificate, but if you're going to do it commercially then you need a commercial certificate. In both cases you also need an agricultural aircraft operator certificate.

An agricultural aircraft operator certificate is required for aerial application, per 14 CFR 137.11. The airman certification requirements are in 137.19:

(b) Private operator—pilot. The applicant must hold a current U.S.
  private, commercial, or airline transport pilot certificate and be
  properly rated for the aircraft to be used.
(c) Commercial operator—pilots. The applicant must have available the
  services of at least one person who holds a current U.S. commercial or
  airline transport pilot certificate and who is properly rated for the
  aircraft to be used.

The FAA's AC 137, Certification Process for Agricultural Aircraft Operators has all the details about how to get an operator's certificate and the airman requirements are in section 2-3. It says:

Pilots designated to conduct operations for the commercial operator
  applicant must hold a current commercial or airline transport pilot
  certificate with the appropriate ratings

A private operator is limited to working his own crops:

Private agricultural aircraft operators may not conduct operations for
  compensation or hire, or conduct operations over a congested area. The
  operator must provide proof of property ownership or other property
  interest in the crop located on that property where the operation will
  be conducted.

By the way, there's no such thing as a "commercial rating" in the US; private and commercial are both certificates.

In the US, you are required to have a commercial license if you fly an aircraft "for compensation or hire". So yes a commercial license is required (in addition to lots of application specific training). I suppose you could dust your own crops without a commercial license depending on how the FAA determines how "compenstaion" applies in that case.

§61.133   Commercial pilot privileges and limitations. (a) Privileges—(1) General. A person who holds a commercial pilot
  certificate may act as pilot in command of an aircraft—
(i) Carrying persons or property for compensation or hire, provided
  the person is qualified in accordance with this part and with the
  applicable parts of this chapter that apply to the operation; and
(ii) For compensation or hire, provided the person is qualified in
  accordance with this part and with the applicable parts of this
  chapter that apply to the operation.

There's an ag school in Waco texas that offers chemical training as well as flight training for a tail dragger. They claim to have you "ready to be employed" when you graduate. So if I got my commercial license and did my schooling there I would essentially be ready to hire out to a ag application business or not?

@JackiKoehn That sounds like it would be a good start. I don’t know the  requirements of individual Ag Application companies so I can’t comment on whether you’d be ready to hire. They may have minimum total hours, tail-dragger hours, and age limits for insurance purposes. FYI to get your commercial license you need 250 hours of flight time.

I did 137 work some time ago, and the insurance company wanted me accident/incident free, with 2500 TT and 1500 in high performance aircraft.  They also wanted 25 hours in type, which was easy as I had flown a Pawnee towing gliders.  My boss had the biggest issue with finding pilots meeting the experience requirements and having a clean accident and enforcement record.  Go figure.